For the future development of a mobile communication system, a D2D technology is introduced to meet user's requirement in a better manner. The D2D technology refers to the data transmission between adjacent User Equipments (UEs) within a short range through a direct link, without any need to being forwarded by a central node (i.e., a base station) nor being transmitted through a conventional cellular link.
For a 3rd Generation Partnership Project (3GPP), a D2D proximity service includes D2D discovery and D2D communication, as shown in FIG. 1.
For the D2D discovery, one UE may determine that another UE is located adjacent to it through an Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN). For example, through the D2D discovery, the UE may search for a taxi or a friend adjacent to it.
For the D2D communication, a network communication link may be converted to a local direct communication link, to save a bandwidth and increase the network efficiency. A link may be directly established between two UEs in proximity to each other (as shown in FIG. 1), so it is able to achieve the communication, through the direct link, between the two UEs which configured to communicate with each other through the network communication link, thereby to provide a communication service in a stable, high-speed and cheap manner. Usually, the proximity service communication is controlled or aided by a network side device, and even an evolved NodeB (eNB) may dynamically allocate resources for the UEs for the proximity service communication.
In the related art, a D2D relay scenario includes a UE-to-network relay scenario and a UE-to-UE relay scenario.
As shown in FIG. 2, for the UE-to-network relay scenario, a remote UE is in an off-network state. Because the remote UE cannot access to the network, and a UE-to-network relay node may function as to enable the remote UE to access to the network for unicast communication. The UE-to-network relay node may route service data related to public safety (including downlink (DL)/uplink (UL) data) between the remote UE and the network.
For the UE-to-UE relay scenario, a public-safety UE may have a relay function. The public-safety UE that has the relay function may be configured to forward data between two public-safety UEs. As shown in FIG. 3, a public-safety UE 1 is not located adjacent to a public-safety UE 2, a public-safety UE 3 is located adjacent to the public-safety UE 1 and the public-safety UE2. In addition, the public-safety UE 3 may have the relay function. In the case that the public-safety UE 1 wants to communicate with the public-safety UE 2, the public-safety UE 3 may serve as the relay node and forward the data between the public-safety UE 1 and the public-safety UE 2.
It can therefore be seen that, in a conventional D2D discovery or D2D communication mechanism, during the proximity discovery procedure, a UE that initiates the communication can merely acquire information about the UEs adjacent thereto, but cannot know which UEs have the relay function, so it is impossible for the UE to select an appropriate UE-to-network relay node or UE-to-UE relay node to access to the network or perform the communication. In addition, there is currently no mechanism for activating or deactivating the relay function of the relay node. Hence, the data transmission efficiency and accuracy for the D2D discovery and D2D communication are severely limited.